Back-to-back HVDC based on Modular Multilevel Converter

This paper focuses on the dynamic performance of an back-to-back HVDC system (HVDC-MMC) using Modular Multilevel Converter (MMC). Based on the proposed Low Frequency Switching (LFS) strategy, including a voltage balancing method, the mathematical model for the HVDC-MMC is developed. Dynamic performance of HVDC-MMC, based on time-domain simulation studies in the PSCAD/EMTDC software tool is evaluated. As a results, it shown that the LFS adopted for MMC-HVDC system can respond satisfactorily during contingencies such as, sudden change on active power flow direction and balanced short circuit at the inverter system side, maintaining balanced voltage at all the dc capacitors.